I did a few tests.
On high gain and low gain. Results were same If not similar.
Andromeda. Stock litz 3.5mm I could not really detect any audiable hiss to my ears. With music playing at various volumes.
With no music and at full volume I still couldnt really hear/detect any hiss.
2.5mm balanced out with ALO Litz.
I could detect and hear hiss at all volumes, the hiss volume didnt really increase with the changes.
The hiss wasnt significant to me as it wasn't so strong and easily went into the background while the music played.
I use the Andromeda a lot as it is one of my favorites and also my reset my ears earphone whilst reviewing. I dont notice hiss much If at all on the many daps I use.
Only on the Hifi-m8 which later had a special lower gain version for iems.
If you are sensitive try the ifi IEMatch ifi ibuddy?
The difference between 1 and 2 ohms output impedance is audiable but not too significant.
The CEntrance has an impedance switch of 1,2,1 which is useful for testing.
@haoyuan
Edit: This made me go back and read my review
I mention about the faint hiss (2.5mm) in the last section.